High quality fuels remain in high demand. Fischer-Tropsch synthesis, which involves the production of hydrocarbons by the catalyzed reaction of mixtures of carbon monoxide (CO) and hydrogen (H2), also referred to as synthesis gas or syngas, can convert natural gas derived synthesis gas to liquid fuels and high-value chemicals. Fischer-Tropsch synthesis is one of the more attractive, direct and environmentally acceptable paths to high quality transportation fuels derived from natural gas.
Fischer-Tropsch catalysts are typically based on group VIII metals such as, for example, iron, cobalt, nickel and ruthenium. Such known catalysts are nonselective for a particularly desired product distribution, namely high levels of C5+ products and low levels of light gas. Processes using such catalysts are generally governed by the Anderson-Schulz-Flory (ASF) polymerization kinetics.
Hybrid Fischer-Tropsch catalyst systems including a Fischer-Tropsch component and an acidic component, such as a zeolite, have been found to be capable of limiting product chain growth in the Fischer-Tropsch reaction to a desired product distribution. Ruthenium, usually known as a promoter for cobalt, is a Fischer-Tropsch active metal that provides surprisingly low methane formation when used as the primary Fischer-Tropsch component. However, certain limitations exist in ruthenium-catalyzed Fischer-Tropsch systems. Ruthenium-catalyzed Fischer-Tropsch products are of much higher molecular weight than those from analogous cobalt-catalyzed reactions, therefore likely to contain a hard solid wax phase. Depending on the proximity of ruthenium to the zeolite pores and the freedom of the ruthenium to migrate into the zeolite channels, high molecular weight wax can form in the zeolite pores and effectively depress the overall catalytic activity.
It would be desirable to have a catalyst system containing ruthenium, with its propensity for low light gas production, and an acidic component which limits product chain growth in the Fischer-Tropsch reaction, while avoiding the limitations caused by ruthenium described above. It would be further desirable to have a process for the conversion of synthesis gas to liquid hydrocarbons in the presence of such a catalyst system to form a liquid hydrocarbon product free of a solid wax phase.